Reenforcement for concrete structures



July 20 1926.

P. J. MARKMANN RBENFORCEMENT FOR CONCRETE STRUCTURES Filed March 2 925 Patented Juiy 20, 19236a v P'HI'LIP J. MARKMANN,

OF- ST. Louis, MISSOURI.

REENFOR'GEMENT r03 oononnrn srnUcTU-nias.

Application ,filed March 2 This invention relates generally to re cniorcenients for concrete structures, and

particularly to combined steel and conc cteiconstruction forcolumns,'or like struc-i fi t1 es, which in service are adapted to withst lnd great compressive stresses in a longitudinal direction. a v

The'iprinciipal object of the invention is to greatly increase the strength o'tt a bar I reenforced concrete column of a given size overthat wli'ich can be attained when "bar re'e' nit'orcements of the types in former and present practice are utilized, and the in rention 1r alize's its greatest advantage because ot' the fact that when it is necessary to provide a column calpable of supporting a predcteri'nined load, a column of the strength necessary to support the designated load may be constructed in accordance with my invention of hycon'siderably smaller diameter than if said column were cons? iructed as heretofore. 1 v In the construction of office buildings, hotels andother large--structures, the question of the loss of space 'due to the presence of manycolumns of relativelylarge diametors is an important one, and it is highly desirable to utilize columns which are as smallas practicable. However, heretofore it has not been possible tored-uce the diameters of bar reenforced:concrete columns because of the physical limitation of the steel bar ratio with the former types of steel bar recniiorcen-ients, which natural limitation oi limitation of thepotenti'al strength of the column. In the use of my improved reeni orce'ment in connection with concrete col n'n'msnthe diameters otsaid columns arere duced to a minimum and muchspace which was tomnerly lost isthereby saved.

Bricfi stated, my invention comprises the u til'i'za "on of the ordinary bar reenforcenient of thetype comprising longitudinal bars and a helically arranged bar associated with said bars. This recni orcementis so arranged that-it located relatively close to the outer face of the colnnni, and because of snch'location and .ofthe cylindricalgshape said reenforcemeut there is a rel atively e space within said reenforce-ment in which no Jreentdrcing bar's heretofore have been located.v In 'c'arrying ont my invention I arrange a second bar reenforcement with the space mentioned, and because ofthe presence Iotrth'rs second reenforcement the the stee'lratio means a correspondingforced 1925. Serial No. 12,558.

strength of the column is materially increased.

I am aware that patents have been granted on IQQllfOiCGIIIGDtS for concrete columns which comprise a reenforcement Within a reen'l orcement, but these reen-forcements have objectionable features in several respects. A disadvantage in connection with the reenitorceinents mentioned is due to the tact that the reenforcing elements are of such shape that the free flow of concrete within the form is interfered with. Another disadvantage is due to the fact that the inner and outer -1-eentorcing elements of the reen-torcements mentioned are in the form of units having;- comparatively large fiat surfaces, and the adherence of the concrete to said surfaces is not as good as that of the concrete to bars. In my in'iproved reenforcement both the outerand inner reinforcing meinbcrs are composed of bars which are spaced-apart from each other a sufficient distance to permit the free flow of concrete therebetwee'n,and also the spaces between the form and the outer skeleton, between the outer and inner skeletons, and inside of the inner skeleton, allow unobstructed passage to the concrete poured into the form.

With the foregoing and other objects in view, the invention con'iprises the novel construction, combination and arrangement 01 parts hereinafter more specifically described and illustrated in the accompanying drawings, wh erein is shown the preferred embodiment of the invention. However, it is-to be understood that the invention conn.)re hends changes. variations and modifications which come within the scope of the claims hereunto appended.

F I is a fragmentary vertical section of a concrete column, or like structure, reen'for-ced inaccordance with my invention.

Fig. 11 is a cross section on the staggered line IIH of Fig. I. v i

Illis a cross section on the staggered line III-J11 of Fig. I.

Fig. IV is an isometric viewof of concrete column reentorced ance with my invention.

In the drawing, A designates a concrete ict-ure which comprisesa footing B, the first filoorslab (ha column D ada pte'd to aid in till-support of the first floor slab (Land a column E which is interposed between said a st floor slab C ,and the next higher a fragment in accord floor slab (wn-otshowi'i). Interposed between the "looting B and the lower end of the cot uinn D is a bed plate 1', said bed plate being adapted to support the entire stack of col.- uinns which extend from the top of said bed plate to the top of the structure. The bed plate 1 may be circular in plan, as shown in Fig. Hi, the particular bed plate illustrated in the drawing comprising hori zontal top and bottom walls 2 and 3 and annular walls 4 and 5 connecting said top and bottom walls together. The bed plate 1 is also provided with an outer upstanding annular flange G, and said bed plate is provided with sets of radial ribs 7 and 8 which, together with. the aforementioned parts, give to the bed plate structure a term adapted to provide for the required strength to withstand the compressive, tensile and shearing stresses to which it is subjected. As shown by the drawing, the bed plate 1 is preferably cast, whereby the various parts of said bed plate are formed integral with each other. In use the cavities within the bed plate 1 are filled with concrete and a body of concrete, annular in shape, is built up outside of the wall 5,.the side face of said body o't concrete being flush with the outer face of the upstanding flange 6 and the top face of said body of concrete being flush with the upper face of the top wall 2 ot the bed plate. 9 designates anchor rods which are embedded in the concrete footing; B and pass through openings in the top and bottom walls 9. and 3 of the bed plate into the column D. It is apparent from the arrangement shown and described that a very substantial base is provided for the stack 0t cohunns, said base comprising the metallic bed plate combined with the concrete and the foundation anchors embedded in the footing below and the. column above and passing through said bed plate.

F designates an outer reentorcing skeleton which comprises a plurality of bars G extended longitudinally of the structure and a helically arranged bar H which encircles said plurality of bars G and is secured thereto in any suitable manner. Reentorc ing skeletons of the type to which the outer reentorcing skeleton F belongs are very well known and have been in connnonuse for some time, and when said reen'torcing skeletons are used in a structure of some height, for instance in a building having a number oi tlcors, said skeletons are madein sections which are superimposed one above the other. When used as an element of my ini proved duplex reentorcement the longitudinal rods G of the reentorcing skeleton F rest upon the upper surface of the top wall 2 of the bed plate 1, as shown in Fig. I, and the upper end portions of said longitudinal rods, conforming to common practice, extend some distance above the top surface of the first floor slab C. The sections of the naeases outer skeleton F extend from the base of the stack of columns to the top thereof, one of said sections bein usually associated with each individual column and the longitudinal rods of each of said sections being extended into the column above the column with which said longitudinal rods are associated (Fig. I) The lower ends of the longit-udinal rods of the sections of the reentorcing skeletons F above the lowermost section rest upon the floor slabs of the building, as suggested by dottedlines in Fig. I, and it is therefore plain that because the upper end portions of the longitudinal rods of the lower section extend abovethe floor slab the upper end portions of the longitudinal rods of thelower section rill overlap the lower end portions of the longitudinal rods of the section immediately above said lower section. This, however, is the usual construction, and it need not be described t'urther, all that need be known being that the longitudinal rods oi adjoining sections overlap each other in a manner to cause the stresses to be transmitted from the rods of the higher section to the rods of the lower section indirectly through the concrete by bond. 7

Located within the cylindrical outer reenlorcing skeleton F is an inner reenforcing skeleton J which comprises a plurality of bars 10 extended longitudinally of the struc ture. As will appear later herein, the inner skeleton, like the outer skeleton, is made in sections which are superimposed one above the other, and the lower ends of the longi tudinal rods of the lowermost section restupon the upper surface of the top wall 2 ot the bed plate 1. Considering the lowermost section of the inner skeleton J, it will be seen that the longitudinal bars 10 extend from the upper sur'"ice of the bed plate 1 to a point slightly above the top face of the first floor slab C. Associated with the longitudinal bars 10 is a plurality o1 spacing rings 11 and 12 in the form of annular members which encircle said longitudinal bars, as shown clearly in Figs. 1, III and IV, said spacing rings being spaced apart from each other in a vertical direction as shown in Fig. I. The longitudinal bars and the spac-- ing rings are secured together, and to effect this connection I employ U-bolts 13 which embrace the longitudinal bars 10 and have threaded end portions which are passed through apertures in said spacing rings and receive nuts 14. It is apparent from this that the elements which make up each section of the inner skeleton J are securely fixed together to produce a rigid unit which may be conveniently handled as a whole, and as'such hoisted above the outer skeleton and lowered into the same into position. Secured to the upper face of the. bed plate 1 is a member 13, having an; upturned annular flange 'Ihe nielnber 13 is so located on the bed'plat'e'l that when the longitudinal bars lO of the lowermost section 'or" the inner reent'orcing skeleton Jare arranged in a clrcle'about theupturned flange 14 thereof and with "the lower ends of said bars in contact with the outer'f'ac'e of said upturned flange, the lower-endo i said lowermost section of said freenforcing skeleton will be properly positionedwith' respect to the bed plate. stitu'tes a means ji'or properly locating the lower'end of the inner skeleton J and also said member 13 prevents the lower end of said skeleton fronrbeing shifted by the concrete'w'henit is poured into the form.

As has been stated herein, the upper end portions offthe longitudinal bars 10 of each sectioufof'tlie inner skeleton 'J extend above the upper surface of the nextffloor slab above the column with which said section is associated, and instead ofoverlapping the end portions ofthe longitudinal bars of adoi'Ihn-g'sections of the 'reentorcing skeleton J as is don'e'in connection with the outer skeleton F, Tabut'the ends of said longitudin'al bars. In this way the compressive stresses :are transmitteddirectly from the longitudinal bars of one section of the reenforceiitent J'to the longitudinal[bars of the next section of said reentorcement instead of through the concrete, as is the case with overlapped joints. To provide'ineans for insuring actual bearing of one bar on another, I employ sleeves 15 (Figs. "I and II), which "encirclethe adj oining ends of "the "bars and are ofsufiicient length to overlap said ends of said bars some distance,'as shown in Fig. I. Atter'the lower column and-the first floorv slab C of "the structure provided with my improved 'reenforceinent has been poured and it is desired'to arrange the second section of the inner reenforcing skeleton in place,'t he sleeves 15 are dropped over the upper end portions of the longitudinal bars ot'thellower sectiomwliidh end portions eXtendabove the upper surface of the floor slabC and are rigidly held thereby. The lower end portions of the longitudinal members ofthe second or uppcr:s'ection are then brought over the upper ends of the sleeves 1'5, and said 'bars'are moved downwardly into said sleeves'uuti'lsaid upperjbars rest upon the top faces of the-longitudinal bars of the lower-section. In this way butt joints are 'made'between the various upper longitudinal bars "and the lower longitudinal bars or adjoining sections of the skeleton J, and the end portions o'f 'said bar's are prevented em being"displaced relative*to each other by the sleeves 15. Connecting the lower ends of the longitudinal, bars of theup'per sections or the upper ends of the longitudinal bars of the lower sections as described also has the e'il'ect of 'preperly locating the In other words, the member 10 conlower en'ddfeach section in its proper cent'ralfipositio'n. To provide for firm contact between the various lOllglttltll'lltll bars of the inner skeleton I provide the ends of said longitudinal bars'with machined faces, and

V to provide firm contact between the longitudinal bars oi the lowermost sections of the outer and inner skeletons with the'bed plate ll provide the top wall 2 of said bed plate and the 'lower'ends of said bars with machined faces.

In erectinga structure "provided with any iin'proved duplex reen forcement, the "outer skeleton F is arranged in position in the usual way and the inner skeleton J is located within said'euter skeleton, "the upper end (it said inner skeleton being temporarily held in its true central position by wires which eX- tend to the form, or to theout-erskeleton. After the form has beenerected the concrete may be poured, and because of the arrange ment of theskeletons and'due to the fact't-hat said slreletonsare made up of properly spaced bars there will be'nothing to interfere ith the free passage the concrete into the form and the free fiow of concrete between and around all bars.

The utilization of a metallic bed plate with a reeniorced -concrete colun'in of the type disclosedherein is a distinct improve nient over the art, for the reason that said bed plate furnishes a bearing of sufficient strength to meet andxresist the relatively high"compressive stresses of "any one all o l the longitudinal fhars square inch for squa'rei'nch. It also furnishes a bearing for the whole compressive stress of the concrete body or the core area of the column. The intensity of this latter stress is only a fraction, sap "one-fifteenth, of "the intensity of the stress transmitted bythe bars, but these two greatly diflering intensities in their travel through the. bed plate are 'c'o'i'iver'ted into a uniform vertical pressure upon the toot'ingdue to the compression, "tensionand shear-resisting strengthoff the bed plate.

In-thecase of a high ratio of longitudinal steel 'ree'nito'rcement, which by my invention may' he easily and practically accomplished,

"the average 'stress over the gross core area of the column will exceed the allowable bearing pressure even upon a surface of eo'ncrete"at least twice the loaded area 'fiecommendations of joint committee and Ahnerichn concrete Institute and special ruling of Cl'i'icag'o buildin department). Even the unit vertical COHlPPBSSlTG stress of the concrete of a column with Spiral "reenforcement of 1% percent, for example, will exceed the allowable bearing pressure upon the concrete of the footin The ineta'llicbed plate is ca able of re eiving thesepre'ssures and of 't'ransi'nitting them to the upper urfgce of the footin'gas a "uniferin'piessureefthe allowable amount pro vided the bearing area of the bed plate is of corresponding size. The necessity of transmitting the column pressure to the footing, partly in bearing and partly by bond on stub bars placed in the footing, or by inter position of a cap block either of a richer mixture of concrete or spirally reent'orccd, together with stub bars which transmit the stress of the steel reenforcement, is entirely eliminated by the use of the metallic bed Jlate 1 between the column and the footing. t is quite plain that the thickness of the footing depends only on the demands of bending and shear stresses developed in spreading the column load from the base area of the bed plate over the required soil area in the case of a spread footing on soil, or over a group of piles, or over a caisson pier, as the case may be. As no stub bars of the types formerly used are utilized in connection with my improved reentoreement, no special depth of the footing need be considered or provided.

The average strength of the gross core area of a column is a function of the unit stress of the concrete either laterally free or restrained and of the longitudinal steel ratio. hen the former is fixed, viz, concrete laterally -free or restrained, the said average strength becomes a function of the remaining variable, the longitudinal steel ratio, and said average strength increases as the said steel ratio increases to a maximum with the greatest practicable or theoretically permissible steel ratio. Practical considerations allow a steel ratio fully as high, and even higher, than that fixed by the Chicago building code (p equals .08) for example, when the column is constructed with my duplex bar reentorcement. Theoretical considerations would allow a steel ratio considerably higher that indicated as advisable by practical considerations of the sizes of the available chutes for dropping and placing the concrete into the form so as to assure a complete saturation of the space surrounding the reenforcing skeletons. It would go beyond the scope of this application to demonstrate the theoretical limit of steel ratio. Suffice it to say here, the theoretical limit is above the practical limit, and the limit of 8 percent fixed by the Chicago building code, -for example, is not too high, rather not high enough. The reentorcing system in use heretofore has simply not allowed even as much as a near approach to that ratio. My invention makes the approach to and even the passing of said steel ratio a matter of relatively simple and easy accomplishment.

I claim l. A reentorcement for concrete structures comprising a reentorcing skeleton formed of bars, and a second reenforcing skeleton within the first mentioned skeleton. said inner skeleton comprising bars extended longitudinally of the structure with which the reenitorcement is associated, members for connecting said longitudinal bars together to produce a unit, and means removable with respect to said members whereby each of said longitudinal bars is individually connected to said members, said means being in engagement with said longitudinal bars and with said members. 2. A reenforcement for concrete structures comprising a reentorcing sleleton formed of bars and a second reentorcin skeleton arranged within the first mentioned skeleton. said inner skeleton comprisingbars extended longitudinally of the structure with which the reeniorcement is associated, annular members associated with said bars, and means supported by said annular mem bers and independently adjustable with re lation thereto whereby said bars and said annular members are connected together.

3. A reeniorcement for concrete structures comprising a reentorcing skeleton composed of bars extended longitudinally of the structure with which the reen'forcement is associated, and circular bars associated with said longitudinal bars, and a second reentorcing skeleton arranged within the first mentioned skeleton, said inner skeleton comprising bars extended longitudinally of the structure with which the reen'l'orcenient is associated, annular members associated with said bars, and fastening devices supported by said annular members and independently adjustable with relation thereto whereby said bars and said annular members are connected together.

4. A ree-ntorcement for concrete structures comprising a reent'orcing skeleton composed of bars extended longitudinally of the structure with which the reentorcement is associated and spiral bars ass0ciated with said longitudinal bars, and a second reelrforcing skeleton arranged within the first mentioned skeleton, said inner skeleton comprising bars extended longitudinally of the structure with which the reenforcement is associated, annular members associated with said longitudinal bars, and U-bolts for connecting said longitudinal bars to said annular members, said U-bolts being capable of independent movement relative to said annular members.

5. A reenforcement for concrete structures comprising a metallic base member on which. said concrete structure is supported, an outer reent'orcing skeleton made in sections arranged one above the other support ed by said base member, and a second reentorcing skeleton arranged within said outer reenforcing skeleton and supported by said base member, said second reenforcing skeleton being made in sections arranged one above the other.

.6. A reenforcement for concrete structin-es comprising a bed plate on which said 7 concrete structure is supported, a footing below said bed plate, an outer reenforcing skeleton supported by said bed plate, an inner reenforcing skeleton within said outer reentorcing skeleton and supported by said bed plate, and an anchor rod embedded in said footing and passed through said bed plate into said concrete structure.

7. A reenforcement for concrete structures comprising a metallic bed plate on which said concrete structure is supported, an outer reeni orcing skeleton composed of bars extended longitudinally of the structure with which the reenforcement is associated and supported by said bed plate, and spiral bars associated with said longitudinal bars, a second reenforcing skeleton arranged within the first mentioned reenforcing skeleton, said second mentioned reenforcing skeleton comprising bars extended longitudinally of the structure with 'which the reen'forcement is associated and supported by said bed plate, annular members associated with said longitudinal bars, and fastening devices for connecting said longitudinal bars to said annular members, said inner skeleton being made in sections arranged in alinement with each other with ends of the longitudinal bars of one section abutting ends of the bars of an adjacent section, and sleeves arranged to encircle and overlap said abut-ting ends of said longitudinal bars. e

In testimony that I claim the hereunto aflix my signature.

PHILIP J. MARKMANN,

foregoing I 

